At present, An intramedullary nail is the main method to fix a fractured long bone to let it heal at present. As shown in FIG. 1, the basic structure of the intramedullary nail includes a long intramedullary nail 11 having an intramedullary nail locking hole 12, and a locking screw 22 corresponding to the intramedullary nail locking hole 12. In the processes to re-connect a broken portion 13 of the long bone 14 and to fasten the intramedullary nail 11, the locking screw 22 has to pass through the intramedullary nail locking hole 12 on the intramedullary nail 11, and has to be locked at one end of the fractured long bone 14. In the situation that the intramedullary nail 11 cannot be seen, it is usually the most time-consuming step in the whole processes to find the exact position and the orientation of the intramedullary nail locking hole 12 which is already inserted into the interior of the long bone 14.
In clinical situations, there are two methods to locate the intramedullary nail locking hole. The first method uses a parallel mechanism to assist in determining the location. The method takes one end of the intramedullary nail that is not inserted into the long bone marrow as a reference point, which is connected to a parallel mechanism to guide to the location. However, the intramedullary nail is forced during the surgery, and thus it is easy for it to be deformed or twisted. For that reason, a location error to the intramedullary nail locking hole can easily be made. Hence, this method is not suitable to a situation where the intramedullary nail locking hole is inserted into the deep interior of long bone marrow. The other method uses X-ray imaging to assist in the location. The photograph of long bone is taken by X-ray, and then the position of the intramedullary nail locking hole in the long bone can be observed directly on the photograph. However, this method causes the patients and the medical personnel to be exposed to radiation, and it causes concern that this method may jeopardize the health of the medical personnel who frequently use this method frequently.
Most location methods without radiation in the prior art can only find the position of intramedullary nail locking hole, but cannot quickly determine the accurate orientation of the intramedullary nail locking hole. Taking the optical location method as an example, a light source is inserted from the end of the intramedullary nail locking hole that does not enter the long bone marrow. When the light source is put at the place near the intramedullary nail locking hole, the light from the light source can be emitted through the intramedullary nail locking hole and through the bone, the tissue and the skin. Finally, a light spot can be seen on the surface of the limb of the patients. The advantage of this location method is that it can be performed quickly, but the disadvantage thereof is that the light spot becomes too large after passing through the tissue and the skin to determine the accurate position and orientation of the intramedullary nail locking hole due to the diffusion of the light spot.
Apart from this, the methods disclosed by the patents that apply the principle of magnetics as the location method are still unable to locate the position and the orientation of the locking hole. For example, a location method disclosed in U.S. Pat. No. 5,411,503 is that during the location procedure, two electromagnets are inserted into the intramedullary nail, and are conducted with the alternating current to generate two alternating electromagnetic fields. The coils aligned in perpendicular to one another outside the intramedullary nail are used to induct the alternating electromagnetic fields. When the induction current in the coils is zero, the location procedure is completed. In this method, the device with high intensity current has to be placed into the body. That causes a safety risk of electric shock. Furthermore, it is necessary to use four outer coils in this method. However, the magnetic fields generated by these outer coils interfere with one another, which could lead to a location error. In addition, during the location procedure, the proper adjustment direction to the location device cannot be obtained. The reduction of the location time is limited due to the trial and error steps that are necessary with this method.
U.S. Pat. No. 5,049,151 discloses an intramedullary nail equipped in its interior with a permanent magnet, and its location device is a magnet set on a universal joint to freely rotate. When the location device gets close to the permanent magnet inside the intramedullary nail, the magnet on the location device is attracted to complete the location procedure. However, in fact, when only a single magnet is adopted in the location device, the given direction only represents the gradient direction of the magnetic field of the permanent magnet. That is not the necessary direction in which the long bone should be drilled. Furthermore, when the single magnet on the location device is attracted by the permanent magnet onto the surface of the long bone, the direction of the single magnet also fails to identify the direction which should be followed to drill. There is still a problem to locate the orientation of the locking hole because the direction which should be followed may not be vertical to the surface of the long bone where the single magnet is attracted.
U.S. Pat. No. 5,514,145, similar to U.S. Pat. No. 5,049,151, discloses that a single magnet is set on a universal joint and an additional location needle. After the location procedure is completed, the location needle is launched to the long bone. However, this method also has the same disadvantages as U.S. Pat. No. 5,049,151.
U.S. Pat. No. 6,162,228 improves the position of the permanent magnet. A slender stick is inserted into an intramedullary nail from the end of the intramedullary nail outside the marrow, and a permanent magnet enters the intramedullary nail along with the slender stick. The position of the permanent magnet deviates a distance from the locking hole, and thus the permanent magnet does not prevent the drill from passing through the locking hole. That allows the bone to be drilled immediately after the location procedure is completed. However, the magnetic location device detects the magnetic field by one single outer magnetic rod as well. It is similar to U.S. Pat. No. 5,049,151 and U.S. Pat. No. 5,514,145. When the single magnetic rod is attracted by the magnetic field, the single magnetic rod indicates only the gradient direction of the magnetic field of the permanent magnet. It only determines the position of the locking hole, but cannot determine the orientation of the locking hole.
In U.S. Pat. No. 7,753,913, an active magnetic sensor array is used, and they are arranged according to the shape of the magnetic field generated by the implanted magnet. The sensor array determines the direction of the magnetic field according to the various magnitudes of the magnetic flux in different positions. When the sensor array detects the same magnetic flux, the location procedure is completed. Operating this system is more complicated and is not direct. The reduction in location time is limited due to the trial and error steps that are necessary when using this device.